Ed Miliband is facing a backlash from Labour MPs and other politicians on Merseyside after he was forced to explain why he had posed for a photograph with the Sun newspaper while the phone-hacking trial and Hillsborough inquest were under way.

Miliband was pictured with a copy as part of a Sun promotion of its support for the England football team during the World Cup in Brazil.

Leading the criticism, Liverpool's Labour, mayor, Joe Anderson, said in a statement: "Like everybody in this city I am really hurt and offended by Ed Miliband's support for the S*n [sic] 'newspaper' today. Such clear support for that publication at any time would be wrong but at such a sensitive time is deeply shocking.

"My city was offended and insulted by the lies and smears peddled by the S*n and their hindrance to our fight for justice is something that will never be forgotten.

"For the leader of the Labour party to make such an offensive gesture insults not only me but every person in the city.

"This is just another example of how out of touch the politicians in their ivory towers are from the lives of ordinary people. It begs the question – were the comments he made after the Hillsborough panel report sincere or just sound bites?"

It is understood Miliband has been criticised in private by Merseyside Labour MPs.

The MP for Liverpool Walton, Steve Rotherham, said on Twitter: "[Miliband] never meant any offence, but in my opinion it shouldn't have happened in the first place". He claimed a statement would be issued by Miliband.

"I hope Ed has a stern team talk with those cheeky monkeys in the press team over why he finds himself in an unnecessary embarrassing situation, again. As any football fan will tell you, too many unforced errors ends in defeat," he wrote.

"It's not easy being leader of the opposition. There is always a conga line of trouble waiting at your office door. You're never far away from disagreement. And in those tiny moments of rest between the ennui of shadow cabinet meetings, there's a helpful spin doctor who can press a promotional copy of the Sun into your hands."

Watson added: "I hope Ed managed to get home in time to have a beer and watch the football if only to take himself away from Twitter, overflowing with discommoded Labour party supporters."

Miliband took the decision to pose with a copy of Britain's most popular newspaper as part of an effort generated by the Sun to support the England team in the World Cup.

Both David Cameron and Nick Clegg, the deputy prime minister, also posed with a copy of the Sun, but many Labour supporters have pointed out the inconsistency between Miliband's tough stance on the need for a public inquiry into phone hacking with cosying up to the newspaper.

The row inside Labour reflects tensions between those that feel that party needs to have as good relations as possible with Rupert Murdoch's newspapers, and those that regard the Sun as beyond the pale.

A Tory source said: "This extraordinary gaffe is proof that Ed Miliband is a weak leader who lacks moral conviction. He is not fit to run his own party, let alone the country."

A Labour spokesman said in a statement that Miliband "was sorry to those who feel offended", but added the Labour leader was promoting support for the England football team and was proud to do so. He added he understood the anger that is felt towards the Sun over the 1989 Hillsborough disaster in which 96 Liverpool football fans died.